1. Field of the Invention
The present invention relates to a method of culturing cells in vitro, and in particular, it relates to a method of culturing cells using hollow fiber membranes.
2. Description of the Prior Art
A primary factor for optimum growth and maintenance of cells is oxygen. Various methods of oxygenating the media have been described. In the Bjorklund U.S. Pat. No. 3,172,235, direct oxygenation of the culturing flask is disclosed. The Michaels et al U.S. Pat. Nos. 4,440,853 and 4,442,206 describe methods of directly oxygenating the media in a reservoir. The Gruenberg U.S. Pat. No. 4,629,686 and the Walker U.S. Pat. No. 4,618,586 describe oxygenating the media in media source vessels.
On-line oxygenation of the media is described in the Weiss et al U.S. Pat. No. 3,407,120 wherein an aeration column is disclosed that oxygenates the media prior to the media being delivered to the cell culturing device. The Knazek et al U.S. Pat. Nos. 3,821,087, 3,883,393, and 4,220,725 describe the use of an oxygenator or artificial lung having a silicone rubber membrane to provide gas transfer for perfusing the media. The Yoshida et al U.S. Pat. No. 4,391,912 describes the use of a hollow fiber cartridge to oxygenate media.
Another method of oxygenating the media on-line is disclosed in the Harm et al U.S. Pat. No. 4,650,766 which describes the use of a gassing block for introducing gas into the media through gas-defusable tubing.
The Noll U.S. Pat. No. 4,514,499 describes a gas permeater that oxygenates the media upstream of a reservoir in a recirculation loop. A pump downstream of the reservoir provides the motive force to deliver the media into a cell culturing device.
The development of culturing cells in vitro has grown tremendously in recent years. One method of cell culturing includes the use of hollow fiber cartridges wherein media is continously transported through the lumen of the hollow fibers while cells are being cultured in an extracapillary space between the hollow fibers and the shell of the hollow fiber cartridge.
In the continuous culturing of cells using hollow fiber cartridges, problems occur in using a highly oxygenated media, that is a media oxygenated near its oxygen saturation level. As the media traverses the wall of the lumen a pressure drop occurs, lowering the oxygen solubility level of the media. This phenomena results in oxygen leaving solution in the extracapillary space. The oxygen then occupies areas within the cell culturing area of the hollow fiber cartridge reducing the space available for the cells to grow.